For many years, an autopsy done by a pathologist was considered the best way to confirm the presence of Alzheimer's disease. But new guidelines proposed on Sunday by the U.S. National Institute on Aging and the Alzheimer's Association seek to distinguish between memory changes or dementia diagnosed by doctors when people are alive, and the changes pathologists can see in an autopsy.

The proposed guidelines will offer additional information about the disease that will help as scientists develop tests that measure biological changes in the brain, blood or spinal fluid to diagnose Alzheimer's at an earlier stage.

Several companies, including Eli Lilly and Co, Bayer and General Electric Co, are working on compounds to identify Alzheimer's-related brain changes on positron emission tomography scans.

Many other companies and researchers are working on other types of biomarkers as well. "Someday, biomarkers are probably going to replace pathology," Dr. Creighton Phelps of the National Institute on Aging's division of neuroscience said in an interview at the Alzheimer's Association International Conference in Paris.

Pathologists now look in the brain for clumps of a protein called beta amyloid and a protein called tau to diagnose Alzheimer's disease.

But studies have shown that people can die with lots of plaques and tangles in their brain and stil have normal cognitive function.

"We know people die with Alzheimer's changes in the brain but they had no dementia," Phelps said.